I carry both CO2 and a "frame pump". It's really just a mini-pump that I carry in my jersey pocket, but it comes with the bits to mount it where the bottle cages go. It's a Topeak Micro Rocket, the aluminum version. $15-19 if you know where to look.
The only thing is, it's a presta valve-only pump. It's not too hard to get to 80-90 PSI.